Term 2 Molecules Tutorial

Question 1

Phospholipids of the bilayer

Answer 1

The phospholipid phosphatidyl ethanolamine (PE) has a conical shape (small head compared to fatty acid tails) it is therefore more easily accommodated in the inner more curves layer of the lipid bilayer. In contrast phosphatidyl choline (PC) is cylindrical ( head same width as tails) and therefore packs more efficiently in flat bilayers.

Question 2

Sterols

Answer 2

Also present in the lipid bilayer:
Ergosterol in yeast (fungi)
Cholesterol in mammals
Stigmasterol in plants.

Sterols are mostly hydrocarbon which is hydrophobic but also have a hydroxyl group that can interact with water making them amphipathic
Sterols intercalate between phospho and sphingolipids preventing gelling (occurs when fatty acid tails are too close together.) Their rigidity maintains structural properties of the bilayer increasing membrane order and Tm (melting temperature) and they may be involved in lipid raft formation.

Question 3

Cisternal progression model

Answer 3

Golgi process - revise.